The present invention relates to a rain sensor which is arranged on the outside of the windshield of a motor vehicle in the region of the windshield wiper and has at least one conductive track which is connected with an electric voltage within the vehicle.
It is known to arrange rain sensors on the windshield of a motor vehicle in the region of the windshield wiper.
These rain sensors give an electric signal to an evaluation circuit within the motor vehicle as a function of the amount of water present at the time on the windshield of the vehicle.
In this connection, the sensors have resistance structures in the form of two strip-shaped conductive tracks which are interlaced in each other. Each conductive track is connected to one potential of the evaluation circuit. If drops of water contact both conductive tracks, a conductive connection is created between them. The total resistance of the sensor structure is thus changed. This change in resistance can be used in order to control a windshield wiper automatically.
In sensors which are located on the outside of the vehicle windshield, the conductive tracks are extended over the edge of the windshield into the inside of the vehicle. In this case, there is the possibility of the conductive track being torn.
The evaluation electronics can, however, not distinguish between a tear of the conductive track and a dry windshield, since a high total resistance of the rain sensor is detected in both cases. If there is water on the windshield, the failure to recognize a tear in the conductive track leads to an incorrect control of the windshield wiper and thus to the danger that the windshield will not be sufficiently cleaned despite the fact that water is present.